This invention relates generally to detection of cancerous cells and more particularly, to detecting cancerous cells using cellular autofluorescence.
The survival rate for cancer patients increases with early detection of cancer. Known methods of gaining early detection of cancer are limited to techniques such as surveillance endoscopy and random tissue biopsies, both of which are costly and inefficient. In addition, methods which employ relatively high levels of radiation which cause tissue damage generally are not preferred. Autofluorescence has been used in attempts to detect cancerous tissue. Particularly, fluorescence occurs when certain substances called fluorophores emit light of a longer wavelength after being excited by light of another, shorter wavelength. The fluorescence which occurs in human and animal tissues is commonly referred to as autofluorescence because the fluorescence results from fluorophores occurring naturally in the tissues. The intensity of autofluorescence differs in normal and cancerous tissues, and autofluorescence can be used to detect cancerous tissue in different organs, including the colon, esophagus, breast, skin, and cervix.
In many medical and laboratory applications, the use of autofluorescence often is preferred for detecting cancerous tissue because autofluorescence avoids the introduction of exogenous fluorophores or any other exogenous agent. The use of exogenous agents increases costs and results in time delays due to lag in incorporating the exogenous agents into the examined tissue. Exogenous agents also introduce the risk of adverse reaction.
Known work on the use of autofluorescence to detect cancer has been limited to examinations of whole tissue in which a decrease in tissue autofluorescence indicates the presence of cancer. However, such work is limited because it relies on measurement of autofluorescence which includes in large part non-specific autofluorescence which is emitted from certain but varied extracellular components of whole tissue. Such extracellular components include blood, blood vessels, collagen and elastin, which all emit autofluorescence. While these extracellular components may change during the progression from normal to cancerous tissue, the changes are not specific to the cells which constitute the actual cancerous tissue. Thus, known uses of autofluorescence to detect cancerous tissue cannot distinguish between specifically cellular changes and non-specific extracellular changes in the progression from normal to cancerous tissue.
It would therefore be desirable to provide apparatus and methods which facilitate the early detection of cancerous cells using autofluorescence. It would also be desirable to provide such autofluorescence apparatus and methods which exclude extracellular changes which are non-specific to cancer. It would further be desirable to provide an objective method for early detection of cancer which is simple to practice and avoids the need for complex, subjective comparisons. It would be yet still further desirable to provide a method for the early detection of cancer which exhibits a reliability which is unaffected by tissue inflammation.
These and other objects may be attained by apparatus and methods for measuring cellular, Tryptophan-associated autofluorescence to enable the early detection of cancerous cells. In one embodiment, the apparatus includes a light source for producing a beam of light to excite a tissue to emit cellular autofluorescence. The beam of light is first filtered through a narrow-band optical filter configured to pass light at a wavelength of about 200 to about 400 nm, which is optimal for producing cellular autofluorescence. The beam of light is then transmitted to the tissue via a two-way fiber optic bundle having a sampling end positioned at or near the tissue being examined. A lens-system is positioned between the sampling end of the two-way fiber optic bundle and the tissue, and the lens system is configured to collect a light sample from the tissue. The light sample is transmitted back through the two-way fiber optic bundle and passes through a narrow-band optical filter configured, in one embodiment, to pass light at wavelengths of about 320-340 nm. A photodetector positioned at the output end of the two-way fiber optic bundle measures the intensity of cellular autofluorescence emitted from the tissue.
In another aspect the present invention relates to a method for detecting pre-cancerous and cancerous cells in a tissue and in one embodiment, the method includes the steps of exciting the tissue with a beam of light delivered through a two-way fiber optic bundle, and measuring the intensity of cellular Tryptopan-associated autofluorescence emitted from the tissue. The two-way fiber optic bundle may be inserted through the biopsy channel of an endoscope, through a laparoscope, or through a needle inserted into the tissue. The light beam has a wavelength of about 200 to about 400 nm, and the light sample is transmitted back through the two-way fiber optic bundle and through a narrow-band optical filter configured to pass light at wavelengths of about 300-400 nm. In an exemplary embodiment the optical filter is configured to pass light at wavelengths of about 320-340 nm, and a filter passing light at wavelengths of about 330 nm is especially suitable.
Measuring the intensity of the light sample at an emission wavelength of about 300-400 nm, and particularly at about 330 nm, enables detection of pre-cancerous and cancerous cells. Specifically, the intensity of the light sample at about 330 nm increases systematically with the progression of cancer from normal to cancerous tissue. Although Tryptophan is believed to be present in some extracellular proteins, it is predominantly present in cells. It is believed that the cell specific fluorescence originates from membranous cellular structures which contain the amino acid Tryptophan. Thus, at the wavelengths identified above, extracellular changes which are non-specific to cancer are largely excluded and therefore, primarily the cellular changes are detected.